The invention relates to a method of manufacturing a wiring system on a supporting body which is provided at least at one surface with a first pattern of electrically conductive material and with a second pattern of electrically conductive material having at least one track crossing the first pattern, in which after providing the first pattern, a layer, termed intermediate layer, of a material which can be etched selectively with respect to the materials of the first and the second pattern is provided over substantially the whole surface, which layer is subjected to a selective etching treatment in which the tracks of the second pattern form an etching mask, in which at the area of the crossing the intermediate layer is removed over an essential part of it thickness and supporting parts are formed from the intermediate layer beyond the said crossing below the second pattern, which parts extend over the whole distance between the second conductor track and the surface of the supporting body or between the second and the first pattern of conductor tracks.
The invention relates in addition to a wiring system manufactured according to such a method, as well as to a semiconductor device having such a wiring system.
Multilayer wiring systems having insulated crossings are known and are generally used in integrated circuits. They increase the freedom of design, in particular when very many circuit elements (transistors, resistors) are integrated in one semiconductor body.
A crossing as described above is generally insulated by air (if desired, vacuum or a filling gas, for example nitrogen). Since the dielectric constant of air (vacuum) is considerably smaller than that of silicon oxide, the parasitic capacitances of such crossings are generally very small compared with those of the usual crossings in which the conductor patterns are insulated by silicon oxide. In addition, short-circuits via so-called pinholes are avoided.
A method as described above is disclosed in applicant's Netherlands Patent Application No. 7608901, which corresponds to U.S. Pat. No. 4,308,090.
In this method an air-insulated crossing is obtained by entirely etching away the intermediate layer below the crossing part of the uppermost conductive pattern. This means that the etching treatment has to be continued until it is sure that the intermediate layer below said crossing part has been removed by lateral etching.
As is also described in said Patent Application, remaining parts of the intermediate layer serve as supporting parts for the second conductive layer. At the location of such a supporting part, the intermediate layer may therefore not be removed entirely during the said etching step. In order to prevent this, the tracks of the second conductive pattern at the area of the supporting part are therefore chosen to be wider than at the area of the crossing so that the intermediate layer below widened parts beyond the crossing is maintained at least partly and locally supports the second pattern of conductive material.
However, this measure causes loss of space in that locally more space is necessary for the conductor tracks. Moreover, for the mutual alignment of the masks defining said widened parts at the area of the crossings, alignment tolerances must be observed.